Math / scientific calculator similar to those from TI, Casio, HP etc

Math / Scientific Calculator

This is a free online math/scientific calculator similar to those from TI, Casio, HP and others. It supports functions for algebra and trigonometry. Enter a formula either by typing on the keyboard, pressing the buttons on the calculator with the mouse, or a mixture of both.

Graphing calculator

This is not a graphing calculator, but see Function Explorer which allows you to graph up to three functions at once with up to three independent variables controlled by sliders.